Conventional forced air heating, ventilating and/or air conditioning (HVAC) systems have manually adjustable air register vents (air volume control dampers) to control the amount of conditioned air introduced into a room or other portion (for simplicity, collectively hereinafter referred to as a “region”) of a building. In theory, the vents may be manually adjusted upon installing the HVAC system or thereafter, so as to provide a correct amount of heated, cooled, filtered, etc. (collectively referred to herein as “conditioned”) air to each region. However, in practice, this seldom works properly. Usually, the registers are not adjusted at all, unless a region is intolerably cold or hot. In addition, it may be impossible to get enough conditioned air to a region without adjusting the registers in every other region. Thus, manually adjusted registers rarely achieve a uniform comfort level throughout a building.
Manually adjusted registers can also waste energy. For example, introducing more conditioned air into a region than is necessary to achieve a comfortable temperature causes a heating or cooling plant to operate longer or at a higher level than would otherwise be necessary. Even if registers have been adjusted to achieve a desired temperature in all regions, the registers may all be closed more than necessary, thus constricting the air flow and increasing pressure in the ducts. This causes the blower that moves the air to do more work than necessary, thereby wasting energy. In addition, the high air pressure in the ducts exacerbates any leaks in the ducts. Such duct leaks frequently allow conditioned air to enter an attic, crawl space or other region that does not need heating or cooling, thereby wasting energy.
Most homes with forced air HVAC systems have only one thermostat. Not only does this mean that only one region actually maintains a desired temperature, it also makes it impractical to adjust the temperature in different rooms to suit the needs of occupants in those rooms. Consequently, room temperatures cannot be personalized.
To overcome some of these problems, some buildings are zoned. Each zone has an associated thermostat to adjust the temperature in that zone. In private homes, this is often implemented by installing a separate HVAC system for each zone. Each zone has its own thermostat, fan, heat exchange, furnace or heat pump, cooling compressor, ducts, etc. This is not only expensive; it can also be extremely wasteful of energy. For example, there is usually nothing to prevent one HVAC zone from heating a portion of a building while another HVAC zone cools another, possibly overlapping, region of the building.
Attempts to solve the multi-zone HVAC problem often include installing a centralized control system coupled to various thermostats and, in some cases, to electrically or pneumatically operated dampers in the ducts. However, such centralized systems require installing wiring to the thermostats, dampers, etc., thereby increasing the difficulty of retrofitting existing buildings. These systems are, therefore, more suitable for new construction than for renovating existing buildings. Furthermore, once such a system is installed, it is difficult to subdivide it into additional zones or to incrementally expand the system.
Prior art electronically controlled register vents for zone heating and cooling are described in U.S. Pat. No. 7,168,627 to Lawrence Kates, et al. A design for a multi-zone HVAC control system from an existing single-zone system using wireless sensor networks is described by Andrew Redfern, et al., in Smart Structures, Devices and Systems III, edited by Said F. Al-Sarawi, Proc. of SPIE, Vol. 6414 (2007). The contents of both these documents are incorporated herein by reference.